It has long been recognized that it is desirable to encapsulate materials so as to protect them from volatilization, the degradation effects of oxygen and heat, moisture, internal and external molecular interactions and the like. Flavors are complex substances made up of multiple chemical components, some comparatively stable, some extremely volatile, others unstable to oxidation and reactive interactions and the like. Many flavorants contain top notes (i.e., dimethyl sulfide, acetaldehyde), which are quite volatile, vaporizing at or below room temperature. These top notes are often what give foods their fresh flavors.
Numerous techniques have been suggested and many commercialized for the encapsulation of flavors. However, all of these techniques suffer from one or more deficiencies. One of the most common techniques for encapsulating flavorants is spray drying. While this process directly produces a finely divided product which can be readily handled and used in the preparation of finished foods, spray drying suffers from several serious deficiencies. First, it is difficult to incorporate top notes into spray dried flavorants in an efficient manner. Inherent in spray drying is the loss of volatile materials. Furthermore, materials which are heat and/or oxygen sensitive are adversely affected by spray drying. The effect of heat, oxygen and volatilization can make a substantial change in the materials' composition, which in turn results in undesirable changes in flavor characteristics.
Freeze-drying solutions of matrix materials containing either dissolved or dispersed flavors has also been used to produce encapsulated flavors. These methods generally result in losses of highly volatile components, and products having a foamy, porous structure.
Yet another technique which has been employed is that of melt encapsulation of materials in carbohydrate matrices. In this application a carbohydrate melt is prepared and the encapsulate is added. The resulting solution is introduced into a quenching medium to produce a solid carbohydrate product containing the flavor. This technique while successful, is again, limited to comparatively high boiling point flavors because the carbohydrate solution is produced and delivered to the quenching medium at elevated temperatures. This technique inherently can result in the loss of some of the low boiling point constituents in the flavor. Because of such losses, it is common to enhance the flavorant by adding extra low-boiling components. The conventional quenching agent which is commercially employed is isopropyl alcohol. The traces of the isopropyl alcohol remaining in the product after quenching can be detrimental. This technique limits the materials which can be encapsulated to those which are immiscible in the matrix. An additional disadvantage of the product resulting from this process is that although reasonably dense, the product may contain microporosity when low boiling point components are present in the flavor. The microporosity increases the surface area, and thus, may increase the evaporation of volatiles and the potential for degradation of the product by interaction with atmospheric oxygen. Furthermore, the effect of the microporosity is enhanced as the product is sold in a finely divided state, which increases the surface area of the particles and thus the possibility that degradation of the flavor will occur if the product is stored over a period of time.
The above encapsulation technology was first developed using batch type melting and mixing equipment. These techniques have been improved as described in U.S. Pat. No. 4,610,890 ('890) and 4,707,367 ('367). In these patents, a process is described for preparing a solid, essential-oil containing composition. This composition is prepared by forming an aqueous, high-solids solution containing a sugar, a starch hydrolysate and an emulsifier. The essential oil is blended with this aqueous solution in a closed vessel under controlled pressure conditions to form a homogenous melt which is then extruded into a relatively cold solvent, normally isopropanol, dried and combined with an anti-caking agent after grinding. A discussion of these and other prior art techniques for encapsulating materials can be found in U.S. Pat. No. 5,009,900. The patents '890 and '367 suffer from the same deficiencies noted in prior art techniques, i.e., loss of volatile compounds and limitations to immiscible flavor encapsulates.
While the above described solidified melt encapsulation technology was first developed using batch type equipment, more recently similar continuous processes have used extruders to produce encapsulated products. One problem encountered in extrusion is the difficulty in obtaining an encapsulant which will melt under reasonable extrusion temperatures. An additional problem with extruded products under typical melting temperatures is that the product will expand and foam upon exit from the extruder head due to expansion of contained volatiles. The objective in encapsulation is to form a hard, dense, glassy type encapsulant. One approach is that described in U.S. Pat. No. 4,820,534 ('534). This patent suggests utilizing as the encapsulant a mixture of two materials, one having a high molecular weight and the other having a low molecular weight; as a result, the mixture may be successfully extruded. During extrusion, according to '534, the minor component melts and the major component dissolves into the minor component. The volatile flavorant becomes dispersed or solubilized within the molten mass which upon cooling produces a single phase matrix. In order for volatile components to be retained, and expansion of the matrix prevented, it is necessary in the process of '534 to minimize the temperature at the extruder head. If the material exits the extruder at a higher temperature, volatiles will be lost from the mixture. The '534 technique needs to utilize as the encapsulant a mixture of materials, one having a melting point sufficiently low such that the remainder will melt into it thereby becoming extrudable under reasonable process conditions.
U.S. Pat. No. 5,009,900 ('900) is directed to a procedure very similar to that of '534 only using a more complex mixture of materials to form the encapsulant material. The '900 patent requires a water-soluble, chemically-modified starch, maltodextrin, corn syrup solids and mono- or disaccharides. The flavorant is mixed into the mixture and the result is extruded.
It would not be possible with either of the techniques of '534 or '900 to encapsulate pure low boiling point materials such as acetaldehyde in a dense matrix at commercially significant loads since the resulting product would foam due to the vaporization of acetaldehyde as it exits the extruder. Furthermore, in both techniques one is restrained by processing considerations in the selection of encapsulate material. Similar techniques are taught in U.S. Pat. No. 4,232,047 ('047). The process of '047 proposes to encapsulate a seasoning or flavoring such as oleoresin, essential oils and the like in a matrix of starch, protein, flour and the like. This technique involves the use of extrusion under high pressure. However, like the other techniques, it is limited in the materials which can be used as the encapsulating agent and the materials to be encapsulated therein. The temperatures involved could cause the loss of volatile top notes.
Another example of the technology which is available is U.S. Pat. No. 4,689,235 ('235) which like '900 and '534 is directed to specific matrix materials for use in encapsulation. This patent relies upon the use of an emulsifier to achieve success.
As evidenced by the foregoing patents, significant effort has been expended in attempting to develop a successful method for encapsulating volatile and/or unstable flavors using solidified melts. These techniques would have the advantage over spray drying in that the product, if a dense matrix can be formed, would not be porous like the spray dried product, thus the flavor encapsulate would be more stable. It would be anticipated that such products would have a long shelf life. However, these technologies do not assure a non-porous product when the pressurized melt exits to ambient pressure and temperature.
In addition to the foregoing deficiencies which have been noted in the prior art techniques, still other deficiencies are that each of these processes is very specific to the encapsulating composition. That is, they significantly restrict the compositions which can be used as encapsulants to a very narrow range.
In producing encapsulated products, it is desirable that the encapsulant have a softening temperature significantly above room temperature. If the softening temperature is low, the material will become tacky, forming lumps which are difficult to handle and process. Patents '534 and '900 suggest utilizing complex mixtures of materials as the encapsulant, such that the resultant matrix is in the glassy state with softening temperatures greater than 40.degree. C.
While solidified melt techniques have, to greater or lesser extent, been utilized commercially to encapsulate some flavorants in dense amorphous matrices, there are many flavorants which simply cannot be encapsulated by existing technology. For example, flavorants which are normally commercially produced in the form of a solution simply cannot be encapsulated at useful levels using existing techniques if the solvent plasticizes the matrix materials. With flavorants such as vanilla extract, it is impossible to remove the water/alcohol solvent without adversely affecting the properties of the vanilla. Even in concentrated form, there still would be appreciable solvent present. Accordingly, vanilla extract has not been successfully encapsulated at commercially useful levels using the above techniques. Therefore, a need exists for a new process to produce dense, non-porous matrices to encapsulate materials that exist in high concentrations of solvents.